1) Field of the Invention
The present invention relates to a process for efficient decomposition treatment of a gas containing fluorine compounds such as C2F6, CF4, C3F8, C4F8, CHF3, SF6, NF3, etc. at a low temperature.
2) Related Art
Fluorine compound gases such as CF4, C2F6, etc. are used in a large amount as a semiconductor etchant, a semiconductor cleaner, etc. However, it was found that these compounds, once discharged into the atmosphere, turn into warming substances causing global warming. Post-treatment of these compounds after their use would be subject to a strict control in the future.
Compounds having a high fluorine (F) content as a molecule constituent such as CF4, C2F6, etc. have a higher electronegativity of fluorine and thus are chemically very stable. From this nature it is very hard to decompose such fluorine compounds, and it is thus in the current situations that no appropriate processes for such decomposition treatment are not available yet.
JP-B-6-59388 (U.S. Pat. No. 5,176,897) discloses a TiO2—WO3 catalyst for hydrolysis of organic halogen compounds. The catalyst contains 0.1 to 20% by weight of W on the basis of TiO2 (i.e. 92% to 99.96% of Ti by atom and 8 to 0.04% by atom of W) and has a decomposition rate of 99% at 375° C. for a duration of 1,500 hours in treatment of CCl4 in ppm order. JP-B-6-59388 suggests that organic halogen compounds having a single carbon atom, such as CF4, CCl2F2, etc. can be decomposed, but shows no examples of decomposition results of fluorine compounds.
JP-A-7-80303 discloses another Al2O3—ZrO2—WO3 catalyst for decomposition of fluorine compound gases. The catalyst is directed to combustion-decomposition of CFCs (chlorofluorocarbons) and has a decomposition rate of 98% for a duration of 10 hours in treatment of CFC-115 (C2ClF5) by combustion-decomposition reaction at 600° C. The disclosed process needs addition of hydrocarbons such as n-butane, etc. as a combustion aid, resulting in a higher treatment cost. Among organic halogen compounds to be treated, fluorine compounds are less decomposable than chlorine compounds. Furthermore, the more the carbon atoms of organic halogen compound, the less decomposable. Decomposition of compounds consisting only of carbon and fluorine such as C2F6, etc. are much less decomposable than CFC-115, but no examples of decomposition results of such compounds are shown therein.